From: David Laight <David.Laight@ACULAB.COM>
To: 'Linus Torvalds' <torvalds@linux-foundation.org>
Cc: Tom Tromey <tom@tromey.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
"Luc Van Oostenryck" <luc.vanoostenryck@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Sparse Mailing-list <linux-sparse@vger.kernel.org>
Subject: RE: [PATCH 00/11] pragma once: treewide conversion
Date: Fri, 5 Mar 2021 09:19:42 +0000 [thread overview]
Message-ID: <44a0cc9cb5344add8ee4d91bffbf958f@AcuMS.aculab.com> (raw)
In-Reply-To: <CAHk-=wh8PptzH-=ak1D7C5Zp6EJ8eurYqVqGdQauupAFaNuG4g@mail.gmail.com>
From: Linus Torvalds
> Sent: 04 March 2021 20:16
>
> On Thu, Mar 4, 2021 at 5:55 AM David Laight <David.Laight@aculab.com> wrote:
> >
> > > (a) the traditional include guard optimization HAS NO HIDDEN SEMANTIC
> > > MEANING. It's a pure optimization that doesn't actually change
> > > anything else. If you don't do the optimization, absolutely nothing
> > > changes.
> >
> > And if the parser is well written the optimisation is probably
> > irrelevant compared to the compile time.
>
> That's actually surprisingly not even remotely true.
The point is that you can skip the unwanted parts of
#if without having to parse the file at all.
You just need to detect the line breaks.
So yes, you need to read the file and look at every byte.
But you don't need to even start tokenising it.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-03-05 9:20 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-28 16:57 [PATCH 00/11] pragma once: treewide conversion Alexey Dobriyan
2021-02-28 16:58 ` [PATCH 01/11] pragma once: delete include/linux/atm_suni.h Alexey Dobriyan
2021-02-28 19:05 ` Jakub Kicinski
2021-02-28 16:59 ` [PATCH 02/11] pragma once: convert arch/arm/tools/gen-mach-types Alexey Dobriyan
2021-03-01 10:19 ` Russell King - ARM Linux admin
2021-03-02 15:15 ` Alexey Dobriyan
2021-02-28 16:59 ` [PATCH 03/11] pragma once: convert arch/s390/tools/gen_facilities.c Alexey Dobriyan
2021-02-28 17:00 ` [PATCH 04/11] pragma once: convert drivers/gpu/drm/pl111/pl111_nomadik.h Alexey Dobriyan
2021-03-01 14:41 ` Linus Walleij
2021-02-28 17:01 ` [PATCH 05/11] pragma once: convert drivers/scsi/qla2xxx/qla_target.h Alexey Dobriyan
2021-02-28 22:07 ` Bart Van Assche
2021-02-28 17:02 ` [PATCH 06/11] pragma once: convert include/linux/cb710.h Alexey Dobriyan
2021-03-03 23:13 ` Michał Mirosław
2021-02-28 17:02 ` [PATCH 07/11] pragma once: convert kernel/time/timeconst.bc Alexey Dobriyan
2021-02-28 17:03 ` [PATCH 08/11] pragma once: convert scripts/atomic/ Alexey Dobriyan
2021-03-01 7:55 ` Peter Zijlstra
2021-02-28 17:04 ` [PATCH 09/11] pragma once: convert scripts/selinux/genheaders/genheaders.c Alexey Dobriyan
2021-02-28 18:37 ` Paul Moore
2021-02-28 18:57 ` Alexey Dobriyan
2021-02-28 17:05 ` [PATCH 10/11] pragma once: delete few backslashes Alexey Dobriyan
2021-03-01 8:54 ` Ido Schimmel
2021-03-02 19:00 ` Vineet Gupta
2021-03-04 14:22 ` Edward Cree
2021-03-23 10:09 ` Pavel Machek
2021-02-28 17:05 ` [PATCH 11/11] pragma once: conversion script (in Python 2) Alexey Dobriyan
2021-02-28 17:11 ` [PATCH 12/11] pragma once: scripted treewide conversion Alexey Dobriyan
2021-03-01 17:35 ` Darrick J. Wong
2021-02-28 17:46 ` [PATCH 00/11] pragma once: " Linus Torvalds
2021-02-28 19:34 ` Alexey Dobriyan
2021-02-28 20:00 ` Linus Torvalds
[not found] ` <877dmo10m3.fsf@tromey.com>
2021-03-03 20:17 ` Linus Torvalds
2021-03-04 13:55 ` David Laight
2021-03-04 20:16 ` Linus Torvalds
2021-03-05 9:19 ` David Laight [this message]
2021-03-05 21:23 ` Linus Torvalds
2021-03-06 13:07 ` Miguel Ojeda
2021-03-06 21:33 ` Linus Torvalds
2021-03-23 10:03 ` Pavel Machek
2021-03-01 0:29 ` Luc Van Oostenryck
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